Stacked vs. Single-Limit UM/UIM Coverage in Illinois

By the FigureMyTax Editorial Team · How we calculate

Stacking adds the uninsured and underinsured motorist limits of several vehicles or policies together. Illinois bars it for UM by statute, and lets a UIM policy limit recovery to the higher single limit.

What stacking means

A household may have more than one vehicle or policy with UM/UIM. Stacking adds those limits after one injury, so $100,000 and $50,000 become $150,000. Single-limit coverage pays only the highest applicable limit.

UM: aggregation is barred

215 ILCS 5/143a(1) says the limits for any coverage for any vehicle under the policy may not be aggregated with the limits for any similar coverage, whether provided by the same insurer or another insurer, applying to other motor vehicles, in determining the total limit available for bodily injury or death suffered by a person in any one crash.

UIM: the policy may limit it

Section 143a-2(5) says nothing prohibits an insurer from providing that if you have coverage under more than one policy or provision, recovery may equal but may not exceed the higher of the applicable limits, and that the limits are not increased because of multiple motor vehicles covered under the same policy. It is permissive: it allows a policy term, and does not itself say what happens without one.

A worked example

Suppose you are an insured under policies with $100,000 and $50,000 of UIM, the at-fault driver paid $25,000 and your damages are $250,000. With a term limiting you to the higher limit, UIM pays $100,000 less $25,000 = $75,000. If your policies had no such term and the limits added up, it could be $150,000 less $25,000 = $125,000. Try your own numbers in the Illinois UM/UIM stacking calculator.

What to check

Read the UIM section and any "other insurance" or limit-of-liability clause in each policy, and ask your insurer in writing which limits it says apply. See what sections 143a and 143a-2 say and how UM and UIM pay differently.

This is general information, not legal advice, and the state comparisons above are illustrative, not an exhaustive survey. Confirm how Illinois's rules apply to your specific case with a licensed Illinois attorney.